Organic electroluminescence devices (organic EL devices), which include organic emitting layers between anodes and cathodes, are known to emit light using exciton energy generated by recombination of holes and electrons injected into the organic emitting layers.
Such an organic EL device is advantageous as a self-emitting device, and expected to serve as an emitting device excellent in luminous efficiency, image quality, power saving and thin design.
For use of an emitting material in an organic EL device, a doping method, according to which a dopant material is doped to a host material, has been known as a usable method.
In order to efficiently generate exciton from injected energy and to efficiently use exciton energy for light emission, the exciton energy generated by the host is transferred to the dopant, so that light is emitted from the dopant.
For instance, fused aromatic compounds and the like having phenanthrene skeletons shown in Patent Documents 1 to 12 have been used as the host or dopant.
However, while there has recently been an increasing demand for organic EL devices excellent in luminous efficiency, heat resistance and lifetime and free from pixel defects, no organic-EL-device material or no host material has been found capable of providing such excellent organic EL devices.
In this respect, in order to enhance internal quantum efficiency and achieve high luminous efficiency, developments have been made on an emitting material (phosphorescent material) that emits light using triplet exciton. In recent years, there has been a report on a phosphorescent organic device.
Since the internal quantum efficiency can be enhanced up to 75% or more (up to approximately 100% in theory) by using such a phosphorescent material, an organic EL device having high efficiency and consuming less power can be obtained.
However, although exhibiting much higher luminous efficiency, traditional phosphorescent organic EL devices have such a short lifetime as to be practically inapplicable.
Patent Document 1: JP-A-2007-84485
Patent Document 2: JP-A-2006-151966
Patent Document 3: JP-A-2005-19219
Patent Document 4: JP-A-2005-8588
Patent Document 5: JP-A-2004-18510
Patent Document 6: WO2007/46658
Patent Document 7: JP-A-2003-142267
Patent Document 8: JP-A-2004-75567
Patent Document 9: WO2006/114966
Patent Document 10: JP-A-2005-197262
Patent Document 11: WO2004/016575
Patent Document 12: WO2006/039982